This invention relates to the recovery of oil from subterranean reservoirs and, more particularly, is concerned with improved waterflooding operations involving the use of hydrocarbyl substituted succinimido aryl sulfonates and/or their corresponding succinamic acid derivatives which are stable to high concentrations of divalent cations and which function as cosurfactants capable of significantly improving the brine stability of other more sensitive surfactants, such as petroleum sulfonates.
In the recovery of oil from oil-bearing reservoirs, it usually is possible to recover only a minor portion of the original oil in place by the so-called primary recovery methods which utilize only the natural forces present in the reservoir. Thus, a variety of supplemental recovery techniques have been employed in order to increase the recovery of oil from subterranean reservoirs. In the supplemental techniques, which are commonly referred to as secondary recovery operations although in fact they may be primary or tertiary in sequence of employment, fluid is introduced into the reservoir in order to displace the oil therein to a suitable production system through which the oil may be drawn to the surface of the earth. The displacing medium may be a gas, an aqueous liquid such as fresh water or brine, an oil-miscible liquid such as butane, or a water and oil-miscible liquid such as alcohol. The most widely used supplemental recovery technique is waterflooding which involves the injection of water into the reservoir.
It has long been recognized that factors such as the interfacial tension between the injected water and the reservoir oil, the relative mobilities of the reservoir oil and injected water, and the wettability characteristics of the rock surfaces within the reservoir are factors which influence the amount of oil recovered by waterflooding. Thus, it has been proposed to add surfactants to the floodwater in order to lower the oil-water interfacial tension and/or to alter the wettability characteristics of the reservoir rock. Also, it has been proposed to add viscosifiers such as polymeric thickening agents to all or part of the injected water in order to increase the viscosity thereof, thus decreasing the mobility ratio between the injected water and oil, and improving the sweep efficiency of the waterflood.
Processes which involve the injection of aqueous surfactant solutions in order to reduce the oil-water interfacial tension are commonly referred to as low tension waterflooding. Thus far, most low tension waterflooding applications have employed anionic surfactants. For example, a paper by W. R. Foster entitled "A Low Tension Waterflooding Process", Journal of Petroleum Technology, Vol. 25, February 1973, pp. 205-210, describes a promising technique involving the injection of an aqueous solution of petroleum sulfonates within designed equivalent weight ranges under controlled conditions of salinity. The petroleum sulfonate slug is followed by a thickened water slug which contains a viscosifier such as a water-soluble biopolymer in a graded concentration in order to provide a maximum viscosity greater than the viscosity of the reservoir oil and a terminal viscosity near that of water. This thickened water slug is then followed by a driving fluid such as a field brine which is injected as necessary to carry the process to conclusion.
A serious limitation encountered in waterflooding with anionic surfactants such as petroleum sulfonates is the tendency of the surfactants to precipitate from solution in the presence of even moderate concentrations of divalent metal ions such as calcium and magnesium ions. Typically, divalent metal ion concentrations of about 50-100 ppm and above cause precipitation of the petroleum sulfonates. Thus, as taught for example in the Foster paper, the surfactant slug may be preceded by a protective slug which functions to displace reservoir waters containing unacceptable amounts of divalent ions ahead of the subsequently injected surfactant slug. Another limitation imposed upon use of anionic surface-active agents resides in the fact that desired low interfacial tensions can seldom be achieved, even in the absence of divalent metal ions, at salinities significantly in excess of 2 or 3 weight percent. Thus, the protective slug as well as the surfactant slug normally will be of a relatively low salinity.
A number of recent patents are directed to low tension waterflooding and surfactant systems which tolerate relatively high salinities and/or divalent metal ion concentrations. For example, U.S. Pat. No. 3,811,504 -- Fluornoy et al is directed to a low tension waterflooding process for use in environments exhibiting a polyvalent ion concentration of about 1500 to about 12,000 parts per million and which employs a three-component surfactant system containing two anionic surfactants and one nonionic surfactant. One of the anionic surfactants is an alkyl or alkylaryl sulfonate and the other anionic surfactant is an alkyl polyethoxy sulfate containing from 1 to 10 ethoxy groups and from 7 to 20 carbon atoms in the alkyl group. The nonionic surfactant may be a polyethoxylated alkyl phenol or a polyethoxylated aliphatic alcohol.
U.S. Pat. No. 3,508,612 -- Reisberg et al is directed to a low tension waterflooding process employing a calcium compatible anionic-anionic surfactant system which can be employed in saline solutions containing from 0.01 to 5 molar NaCl and from about 0 to 0.1 molar CaCl.sub.2. One of the anionic surfactants employed in the Reisberg et al process is an organic sulfonate such as petroleum sulfonate having an average molecular weight within the range of 430-470 and the other surfactant is a sulfated ethoxylated alcohol. A preferred sulfated alcohol is one containing a C.sub.12 -C.sub.15 alkyl group and three ethylene oxide groups.
Another technique involving the use of calcium-compatible surfactant systems in low tension waterflooding is disclosed in U.S. Pat. No. 3,827,497 -- Dycus et al. In that patent, the patentees disclose a process in which a three-component or two-component surfactant may be employed. The three-component system comprises an organic sulfonate surfactant such as petroleum sulfonate, a polyalkylene glycol alkyl ether, and a salt of a sulfonated or sulfated oxyalkylated alcohol. The two-component system comprises an organic sulfonate surfactant and a salt of a sulfonated oxyalkylated alcohol. These surfactant systems may be employed in a brine solution which will usually contain about 0.5-8% sodium chloride and will often contain 50-5,000 ppm polyvalent metal ions such as calcium and/or magnesium ions.
Hydrocarbyl substituted succinimido phenyl monosulfonates which are described as having detergent properties at high temperatures, especially when incorporated in oil or fuel compositions, are disclosed in British Patent Specification No. 1,194,286. However, the British patent is unconcerned with waterflooding and neither discloses nor suggests the novel hydrocarbyl substituted succinimido aryl di- and tri-sulfonates, or the corresponding succinamic acid derivatives which form a preferred embodiment of the present invention.